Graphene reinforced materials and related methods of manufacture

ABSTRACT

Graphene reinforced materials and related methods of manufacture are provided. The graphene reinforced materials include graphene sheet or scroll, graphene-polymer sheet or scroll, and graphene-carbon sheet or scroll, each having material properties that are attractive across a broad range of applications and industries. The graphene reinforced materials generally include monolayer or multilayer graphene that is synthesized by annealing a catalyst substrate within a CVD chamber, introducing a hydrocarbon gas as a carbon source with the CVD chamber to form a layer of graphene on the catalyst substrate, detaching the catalyst substrate from the layer of graphene, and rolling the layer of graphene onto itself to form a scroll, optionally with the addition of a polymer layer or carbonized layer on the graphene layer.

This invention was made with government support under Contract No.DE-AC05-00OR22725 awarded by the U.S. Department of Energy. Thegovernment has certain rights in the invention.

BACKGROUND OF THE INVENTION

The present invention relates to graphene reinforced materials andrelated methods of manufacture.

Graphene is an individual layer of carbon having a hexagonal bondingstructure in a one-atom thick sheet. Graphene is known to exhibit lowdensities (<0.77 mg/m²) and a high tensile strength (>130,000 MPa). Thetensile strength of graphene is greater than that of carbon steel (850MPa), diamond (2,800 MPa), aramid (3,700) and carbon fiber (6000 MPa).In view of the desirable mechanical properties of graphene, a reliabletechnology for the scalable production of graphene articles is desired.

One known technique for graphene production includes mechanicalexfoliation of graphite crystals. However, graphene produced by thismethod yields unconnected micrometer-sized graphene crystals in a powderform which has certain limitations in material reinforcementapplications. Another known technique includes chemical vapor depositionat low pressures. According to this method, a metal substrate isannealed in a reducing atmosphere. After annealing, the metal substrateis exposed to a carbon source in a low pressure reactor to synthesizegraphene. A variety of organic gases and solids can be used as thecarbon source for graphene growth, with methane gas being a widely usedprecursor. However, the metal substrate can be difficult to feed intothe low pressure reactor, accompanied by severe evaporation of the metaland the requirement of a vacuum system compatible with flammableprecursor gases.

SUMMARY OF THE INVENTION

Graphene articles and related methods of manufacture are provided. Thegraphene articles include for example substantially pure graphenescroll, graphene reinforced sheet, and graphene reinforced scroll (alsoreferred to herein as graphene reinforced fiber and graphene reinforcedthread), each having material properties that are attractive across abroad range of applications and industries. The graphene articlesgenerally include monolayer or multilayer graphene that is grown bychemical vapor deposition (CVD), optionally at atmospheric pressure.

In one embodiment, a substantially pure graphene scroll is provided. Thesubstantially pure graphene scroll is cylindrical and has a spiralcross-section with multiple internal walls, providing a yield tensilestrength greater than 10 GPa in some applications. A method for formingthe graphene scroll includes annealing a catalyst substrate within a CVDchamber, introducing a hydrocarbon gas as a carbon source with the CVDchamber to form at least one layer of graphene on the catalystsubstrate, dissolving the catalyst substrate from the at least one layerof graphene, and rolling the at least one layer of graphene onto itselfto form a scroll. This method can optionally include delaminating thegraphene layer from the catalyst substrate, for example electrochemicaldelamination, as an alternative to dissolving the catalyst substrate.

In another embodiment, a graphene-polymer sheet is provided. Thegraphene-polymer sheet includes a graphene layer and a polymer layerextending over a major surface of the graphene layer. Thegraphene-polymer sheet is optionally rolled into a cylindrical scrollhaving a spiral cross-section with multiple internal walls. A method forforming a graphene-polymer sheet includes annealing a catalyst substratewithin a CVD chamber, introducing a hydrocarbon gas as a carbon sourcewith the CVD chamber to form at least a layer of graphene on thecatalyst substrate, depositing a polymer film onto the layer ofgraphene, and detaching the catalyst substrate from the layer ofgraphene. The polymer film can include lignin, polyacrylonitrile,polymethyl methacrylate, polystyrene, polycarbonate, polyimides,polypropylene, polyethylene terephthalate, polyvinylchloride and others.The graphene reinforces the polymer film, while also functioning as atemplate which aligns polymer chains during fabrication.

In another embodiment, a graphene-carbon sheet is provided. Thegraphene-carbon sheet includes a graphene layer and a carbon layerextending over a major surface of the graphene layer. Thegraphene-carbon sheet is optionally rolled into a cylindrical scrollhaving a spiral cross-section with multiple internal walls. A method forforming the graphene-carbon sheet includes annealing a catalystsubstrate within a CVD chamber, introducing a hydrocarbon gas as acarbon source with the CVD chamber to form at least one layer ofgraphene on the catalyst substrate, depositing a polymer film onto thelayer of graphene, and heat treating the polymer film to carbonize thepolymer.

These and other features and advantages of the present invention willbecome apparent from the following description of the invention, whenviewed in accordance with the accompanying drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating a method for the controlledsynthesis of large area single-layer or multi-layer graphene for agraphene scroll.

FIG. 2 illustrates a substantially pure graphene sheet orgraphene-polymer sheet being rolled into a multi-wall scroll.

FIG. 3 is a flow chart illustrating a method for the controlledsynthesis of a graphene-polymer composite.

FIG. 4 illustrates a cross-section of a composite formed according tothe method of FIG. 3.

FIG. 5 is a flow chart illustrating a method for the controlledsynthesis of a graphene-carbon composite.

FIG. 6 illustrates a cross-section of a composite formed according tothe method of FIG. 5.

FIG. 7 is a strain-force curve for pure PMMA scrolls illustrating anaverage force value of 35 gf for failure.

FIG. 8 is a strain-force curve for graphene-reinforced PMMA scrolls(atmospheric pressure CVD) illustrating an average force value of 65 gffor failure.

FIG. 9 is a strain-force curve for graphene-reinforced PMMA scrolls (lowpressure CVD) illustrating an average force value of 65 gf for failure.

FIG. 10 is a strain-force curve for graphene-reinforced PMMA scrolls(low and atmospheric pressure CVD) illustrating an average force valueof 65 gf for failure.

DETAILED DESCRIPTION OF THE CURRENT EMBODIMENTS

The current embodiments include substantially pure graphene scroll,graphene reinforced sheet, graphene reinforced scroll, and relatedmethods of manufacture. As set forth more fully below, the graphenescroll, the graphene reinforced sheet, and the graphene reinforcedscroll are formed by CVD deposition, optionally achieving a tensilestrength that exceeds that of carbon fiber and aramid, and includingmaterial properties that are attractive across a broad range ofapplications and industries.

Referring now to FIG. 1, a flow chart illustrating graphene scrollformation is illustrated. In general terms, a method for forminggraphene scroll in accordance with one embodiment can include thefollowing steps: a) annealing a catalyst substrate within a CVD chamber,b) introducing a hydrocarbon gas as a carbon source with the CVD chamberto form at least a layer of graphene on the catalyst substrate, c)detaching the catalyst substrate from the at least one layer ofgraphene, and d) rolling the at least one layer of graphene onto itselfto form a scroll.

Annealing the catalyst substrate is depicted as step 10 in FIG. 1. Thecatalyst substrate includes a dimensionally stable sheet material forsynthesizing graphene thereon. The sheet material includes copper foilin the present embodiment, but can include other materials in otherembodiments. For example, the sheet material can include nickel, iron,cobalt, platinum, silicon, silicon carbide, silicon dioxide, siliconnitride, hafnium oxide, zirconium oxide, boron oxide, magnesium oxide oraluminum oxide. The copper foil is optionally a “low” purity copper foilwith an impurities content up to 10% (e.g., 0.0025 mm thick 99.8% copperfoil, available from Alfa Aesar of Ward Hill, Massachusetts as #13382)or a “high” purity copper foil (e.g., 0.0025 mm thick 99.999% copperfoil, available from Alfa Aesar of Ward Hill, Mass. as #10950).

Annealing conditions can be selected to promote graphene grain growth,avoid vaporization of the catalyst substrate, and avoid substantialsurface oxidation of the catalyst substrate. The annealing conditionsinclude an annealing temperature, a temperature ramp rate, and anannealing duration. For example, annealing can occur at a temperaturebetween about 600° C. to about 1100° C., with a temperature ramp ratefrom about 10° C./min to about 1000° C./min, and an annealing durationfrom about 1 minute to about 120 minutes. In the current embodiment,annealing is generally performed in a CVD chamber in the presence ofhydrogen gas at atmospheric pressure. In other embodiments, annealing isperformed at atmospheric pressure in the presence of one or more noblegases e.g., helium, neon, argon, or xenon, or in the presence of aninert gas such as nitrogen. Alternatively, annealing can be performed ina low pressure environment or in a vacuum environment within a CVDchamber.

Introducing a hydrocarbon as a gas source is depicted as step 12 inFIG. 1. The hydrocarbon includes methane in the present embodiment, butcan additionally or alternatively include ethane, propane, and butane,for example. The hydrocarbon interacts with the upward facing surface ofthe annealed substrate within a quartz CVD chamber for the controlledformation of large-area (e.g., >1 mm) graphene on the annealedsubstrate. The hydrocarbon forms part of a reaction gas mixture, whichoptionally includes hydrogen and further optionally includes a buffergas. Hydrogen can be present in the reaction gas mixture with a partialpressure of between about 0 Torr and about 25 Torr, further optionallybetween about 10 Torr and about 25 Torr, still further optionallybetween about 25 Torr and about 500 Torr, and even further optionallyabout 760 Torr. Methane can be present in the reaction gas mixture witha partial pressure of between about 20 mTorr and about 10 Torr, furtheroptionally between about 23 mTorr and about 100 mTorr. Hydrogen having apartial pressure ratio P_(H2)/P_(CH4)>200 can result in a distincthexagonal shape of grains as set forth in U.S. Patent ApplicationPublication 2013/0174968 to Vlassiouk et al, filed Jan. 4, 2013, thedisclosure of which is incorporated by reference in its entirety. Thebuffer gas can include argon or other noble gas (e.g., helium) ornitrogen to maintain atmospheric pressure within the CVD chamber.

Detaching the catalyst substrate from the at least one layer of grapheneis depicted as step 14 in FIG. 1. This step includes any technique bywhich all or a portion of a catalyst substrate is removed from the atleast one layer of graphene. For example, this step can includedissolving the catalyst substrate according to a chemical etchingprocess. This step can alternatively include other processes withoutcomplete catalyst dissolution, such as electrochemical delamination. Inembodiments where the catalyst substrate is dissolved, step 14 caninclude the use of a ferric chloride (FeCl₃) solution, a hydrogenchloride (HCl) solution, a presulfate solution, or other catalystetchants. For example, the graphene-copper article, once removed fromthe CVD chamber, can be submerged in a temperature-regulated FeCl₃solution for approximately one minute to several hours to remove thecopper substrate from the graphene-copper article. Also by example, thegraphene-copper article, once removed from the CVD chamber, can besubmerged in a temperature-regulated Na₂S₂O₈ solution for approximatelyone minute to several hours to remove the copper substrate from thegraphene-copper article. Other solutions can be used in otherembodiments where desired, for example where the substrate is other thancopper.

Consolidating or rolling the graphene layer onto itself to form a scrollis depicted as step 16 in FIG. 1, and illustrated in FIG. 2. This stepcan include floating the substantially pure graphene layer (i.e.,substantially free of catalyst substrate and polymer) on a watersolution surface. The graphene layer is then “scrolled” or rolled inwardor outward onto itself multiple times. Alternative techniques includesingle-sided hydrogenation as disclosed in “Hydrogenation EnabledScrolling of Graphene” in J. Phys. D: Appl. Phys. 46 (2013) by Zhu etal, and sonication as disclosed in “A Chemical Route to CarbonNanoscrolls” by Viculis et al (2014), the disclosures of which isincorporated by reference in their entirety. The resulting graphenescroll (also referred to as a thread or a fiber) includes asubstantially cylindrical shape with a spiral cross-section, e.g.,having multiple internal walls of graphene film.

The above embodiment therefore provides a method of preparing asubstantially pure graphene scroll. The graphene scroll can have a yieldtensile strength greater than 1 GPa, optionally greater than 10 GPa(e.g., between 10 GPa and 30 GPa), and further optionally greater than30 GPa (e.g., between 30 GPa and 50 GPa). The graphene scroll caninclude graphene crystals having hexagon or star-like grains with anaverage grain size sizes of 1 μm to 1 cm, optionally 1 μm to 1 mm,further optionally 1 μm to 100 μm, and still further optionally 1 μm to10 μm. The graphene can include spectra intensity ratios of I_(D)/I_(G)less than or equal to 1, less than or equal to 0.1, less than or equalto 0.01, and less than or equal to 0.001, for example.

The graphene scroll can include single-layer or multi-layer grapheneformed on (and later detached from) various catalyst substrates (e.g.,copper, nickel, cobalt, iron) and rolled up to form the graphene scroll.The above embodiment can be modified to include a polymer layer or acarbon layer, forming “heterostructures” or “composites.” The compositescan include single-layer graphene and/or multi-layer graphene.Multi-layer graphene can be prepared by the consequent transfer ofseveral graphene layers on top of each other or growing multi-layergraphene directly on a catalyst substrate.

More particularly, and with reference to FIG. 3, a flow chartillustrating formation of a graphene-polymer composite is illustrated.In general terms, a method for forming the graphene-polymer composite issimilar to the method of FIG. 1, and includes deposition of a polymer orpolymers on the synthesized graphene. The step is depicted as step 18 inFIG. 3. The polymer can include lignin, polyacrylonitrile (PAN),polymethyl methacrylate (PMMA), polystyrene, and polycarbonates, forexample. Deposition of the polymer can include, for example, spincoating, spray coating, deep coating, and plasma polymerization, forexample. Other deposition methods can be used in other embodiments asdesired. Polymer deposition can occur prior to detaching of the catalystsubstrate as shown in FIG. 4, or after detaching of the catalystsubstrate. To reiterate, “detaching” as used herein includes anytechnique by which all or a portion of a catalyst substrate is removedfrom a graphene layer. Detaching includes, for example, dissolving allor a portion of the catalyst substrate, optionally according to achemical etching process. Detaching also includes, for example,delaminating all or a portion of the catalyst substrate, optionallyaccording to electrochemical delamination.

The sheet composite is optionally rolled onto itself to form a thread asdepicted as step 16 in FIG. 3. This step can include floating thecomposite on a water solution before rolled inward or outward ontoitself multiple times. The resulting scroll includes a substantiallycylindrical shape with a spiral cross-section, e.g., having multipleinternal walls of graphene film and polymer. The thickness of thepolymer is optionally between about 20 nm and 10 μm inclusive, furtheroptionally between about 100 nm and 500 nm inclusive, and still furtheroptionally about 200 nm. The thickness of the graphene layer isoptionally less than 20 nm in some embodiments, further optionally lessthan 10 nm, and even further optionally less than 3 nm.

After polymer deposition, and before scrolling, the polymer can be heattreated to carbonize the polymer as optionally shown in step 20 of FIG.5. For example, a suitable carbon fiber precursor (e.g., PAN) can be (a)heated in air to a temperature ranging from 200° C. and 300° C. to formbonds between individual polymeric chains and (b) heated under inertconditions to a temperature ranging from 1000° C. to about 3000° C. toalign the polymer chains. Carbonization can continue for a dwell periodtypically measured in minutes, resulting in the cross-linking of PANfibers to achieve carbonized filaments. The resulting composite sheetincludes mono-layer or multi-layer graphene, a carbonized PAN layer, andan optional substrate, illustrated in FIG. 6. The composite sheet can berolled as depicted as step 16 in FIGS. 1 and 3, optionally afterdetaching the optional substrate at step 14 of FIG. 5. This step caninclude floating the composite on deionized water. The composite is then“scrolled” or rolled inward or outward onto itself multiple times. Theresulting graphene reinforced carbon scroll includes a substantiallycylindrical shape with a spiral cross-section, e.g., having multipleinternal walls of mono-crystalline graphene and carbon.

Example

Graphene-acrylic scrolls were synthesized according to the followingmethod, described with reference to FIGS. 7-10, which is intended to benon-limiting.

Graphene was synthesized by chemical vapor deposition under bothatmospheric pressure and low pressure using methane as a precursor andusing copper foil as a base layer. PMMA 495A4 solution available fromMicroChem Corp. of Newton Mass. was spincoated at 2000 rpm on thecopper-graphene sample. The copper base layer was then dissolved in 0.1MFeCl₃, which resulted in a graphene-reinforced PMMA sheet (PMMA having athickness of about 200 nm). The graphene-reinforced PMMA sheet wasfloated on deionized water and rolled up to form a scroll.

Tensile strength was measured for the graphene reinforced PMMA scrollagainst unreinforced (e.g., pure) PMMA scrolls. Tensile strengthmeasurements are depicted in FIG. 7 for pure PMMA scrolls. The averageforce value required to break the unreinforced PMMA scrolls was 35 gf(0.34 N), corresponding to a tensile strength of 34 MPA as shown inEquation 1 below, where F is the applied force and A is thecross-sectional area of the PMMA scroll:σ=F/A=0.34N/(0.05 m*200E−9 m)=34 MPa  (1)Tensile strength measurements for graphene-reinforced PMMA are depictedin FIGS. 8, 9 and 10 corresponding to graphene CVD synthesis atatmospheric pressure and low pressure, respectively. The average forcevalue required to break graphene-reinforced PMMA scrolls was 65 gf (0.64N), shown in FIG. 10. The graphene layer contributed 30 gf of strengthto the PMMA scroll, corresponding to a tensile strength of 18 GPa asshown in Equation (2) below:σ=F/A=0.3N/(0.05 m*0.34E−9 m)=18 GPa  (2)

Preliminary data suggested that even non-optimized conditions forgraphene synthesis can yield materials with a tensile strength of 18GPa, which is approximately 15% of the maximum theoretical value, fivetimes stronger than aramid and three times stronger than carbon fiber.

The above description is that of current embodiments of the invention.Various alterations and changes can be made without departing from thespirit and broader aspects of the invention as defined in the appendedclaims, which are to be interpreted in accordance with the principles ofpatent law including the doctrine of equivalents. Any reference toelements in the singular, for example, using the articles “a,” “an,”“the,” or “said,” is not to be construed as limiting the element to thesingular.

The invention claimed is:
 1. A method of forming a graphene scroll, themethod comprising: inserting a catalyst substrate into a chemical vapordeposition chamber, the catalyst substrate being a sheet material offreestanding metal foil; annealing the catalyst substrate in hydrogengas within the chemical vapor deposition chamber; and exposing theannealed catalyst substrate to a reaction gas mixture including ahydrocarbon; synthesizing graphene from the reaction gas mixturefollowing the exposure of the annealed catalyst substrate to thereaction gas mixture; detaching the annealed catalyst substrate from thesynthesized graphene; and consolidating the synthesized graphene byfloating the synthesized graphene on a solution and rolling thesynthesized graphene onto itself to form a cylindrical multi-wallgraphene scroll having a spiral cross-section, wherein the synthesizedgraphene is a non-hydrogenated graphene layer at least duringconsolidation into the multi-wall graphene scroll.
 2. The methodaccording to claim 1 further including bonding a polymeric film to thesynthesized graphene prior to consolidation into a multi-wall graphenescroll.
 3. The method according to claim 2 further including heattreating the polymeric film to carbonize the polymeric film.
 4. Themethod according to claim 1 wherein the hydrocarbon is selected from thegroup consisting of methane, ethane, propane, butane, pentane, hexane,heptane, octane, acetylene, benzene, toluene and combinations thereof.5. The method according to claim 1 wherein the freestanding metal foilis a copper foil.
 6. The method according to claim 1 wherein annealingthe catalyst substrate includes gradually heating the catalyst substrateto approximately 1000° C.
 7. The method according to claim 1 wherein thereaction gas mixture includes a buffer gas selected from the groupconsisting of noble gases and nitrogen.
 8. A method of synthesizing agraphene article, the method comprising: passing a metal substratethrough a heated chemical vapor deposition chamber at atmosphericpressure, the metal substrate being a sheet material of freestandingmetal foil; introducing hydrocarbon gas as a carbon source to form atleast a monolayer of large area graphene including crystal hexagonalgrains on the metal substrate; forming a thermoplastic film on a surfaceof the graphene opposite the metal substrate; detaching the metalsubstrate from the graphene to achieve a composite graphene article; andconsolidating the composite graphene article by floating the compositegraphene article on a solution and rolling the composite graphenearticle into a cylindrical multi-wall graphene scroll having a spiralcross-section, wherein the graphene of the composite graphene article isa non-hydrogenated graphene layer at least during consolidation into themulti-wall graphene scroll.
 9. The method according to claim 8 furtherincluding heat treating the polymeric film to carbonize the polymericfilm.
 10. The method according to claim 8 wherein the thermoplastic filmincludes poly(methyl methacrylate).
 11. The method according to claim 8wherein the thermoplastic film is spin coated, spin coated or deepcoated onto a surface of the graphene opposite the metal substrate. 12.The method according to claim 8 further including continuouslyextracting the metal substrate from the chemical vapor depositionchamber.